1. Field of the Invention
The invention relates to the field of automating testing of complex equipment including electrical and optical components, and in particular to an apparatus and method for testing a multiple discrete analyzer (MDA) optical module.
2. Background Information
A multiple discrete analyzer, referred to hereafter as an MDA, is a complex machine for automatically performing multiple coagulation related diagnostic tests on human blood. An example of such a machine is described in U.S. Pat. No. 5,002,392, assigned to the assignee of the present application, hereby incorporated by reference.
Briefly, the MDA includes a multi-channel optical monitoring system for monitoring the spectral transmission of a plurality of blood samples. A plurality of light beams are generated and a plurality of optical monitoring stations (positions) are arranged along a pathway. Each station has an optical path formed by one of the light beams transverse to the pathway. The optical characteristics are monitored along the optical path at each station. A drive mechanism moves a plurality of reaction wells, each containing a reaction volume (blood sample), along the pathway from station to station. The respective reaction volumes dwell periodically at each station in each respective optical path transmitting a respective one of the light beams. A diffraction grating is provided for diffracting the beams transmitted by respective ones of the reaction volumes. The diffracted beams are focussed and at least one array of photodetectors is positioned for receiving the diffracted and focussed beams for producing electrical signals representing the spectral content of the diffracted beams. An electronic circuit detects the electrical signals of the array which may be stored for further processing and evaluation.
The multi-channel optical monitoring system includes a plurality of photodiode arrays illuminated by light beams projected onto the arrays by way of a shutter mechanism. Each of the light beams constitutes an optical channel and passes through a reaction well of a cuvette and then through a transmitting diffraction grating for the purpose of performing an optical analysis of a reaction volume, the blood sample, in the reaction well. The photodiode arrays each develop electrical signals corresponding to the spectral distribution of the respective beams falling on the arrays, and the arrays are periodically read by electronic scanning circuitry.
The disclosed shutter mechanism comprises a rotating shutter which includes a number of cam elements mounted on a motor driven shaft. The light beams are incident on the cams in a direction parallel to the rotational planes of the cams. Each cam element is aligned in a respective one of the optical channels and has a cut-out segment greater than 180.degree. so that each cam will block the light beam that it is aligned with for a certain portion of the rotation and will pass the beam for a remaining portion of the rotation. The cut-out segments of the cams are angularly arranged relative to one another so that the rotating shutter sequentially passes the beams in a predetermined sequence.
Each cam thus constitutes a shutter element which opens and closes an optical path during each revolution. Actually, each revolution of a cam may be divided into four periods. A first period occurs during a portion of a turn when the cam completely blocks the optical path of the light beam. A second period occurs when an edge of the cam bordering on the cut-out segment passes through the optical path of the beam during which the optical beam is partially transmitted onto the photodiode array. This is the opening transition. A third period occurs at the conclusion of the opening transition when the cut-out segment of the cam is positioned so that the optical path of the beam is uninterrupted by the cam and therefore the entire beam is fully projected onto the photodiode array. The fourth period is the closing transition period when the other edge of the cut-out segment passes through the optical path of the beam so that the optical beam is again only partially transmitted onto the photodiode array. At the conclusion of the closing transition period the optical beam is totally blocked so that the optical channel enters into a dark period (the first period described above) until the next opening transition period.
The electronic scanning circuitry disclosed in U.S. Pat. No. 5,002,392 involves a charge storage mode of operation whereby each photodiode element integrates light projected thereon by virtue of an electron depletion of its p-n junction which is replenished at the time of scanning. The amount of charge required to replenish the electron depletion is a measure of the integrated light. The charge coupled mode of operation for electronically scanning a photodiode array is well known as disclosed in U.S. Pat. No. 5,002,392 and the prior art cited therein.
The charge storage mode of operation for scanning the photodiode arrays is desirable in an environment in which there are hundreds of low level optical signals that must be evaluated at high speeds and is economical in terms of cost and space since only a single charge coupled amplifier is required in lieu of a separate amplifier for each photodiode element.
Electronic control, interfacing and processing circuitry is associated with the above optical module components. The circuitry includes shutter rotation control circuitry, filter selection control circuitry, photodetector scanning and control circuitry, photodetector signal amplification circuitry, digital to analog and analog to digital convertor devices and other interface circuitry.
The above optical, electronic, and optoelectrical elements comprise the optical module of the MDA. The optical module is the critical element of the MDA and proper operation of the MDA is dependent on proper alignment and operation of the optical module. In the past, testing and alignment of the completed optical module has represented an insurmountable task given the large number of variables affecting its operation. Tests and adjustments had to be made during assembly of each portion of the module, resulting in increased manufacturing time and costs.
Testing and alignment of the completed optical module should ideally include testing and adjusting the sensing and control electronics, testing for light leakage, wavelength registration and testing, optical uniformity stability and alignment, and filter testing.
A need has, therefore, existed for an efficient, accurate and automatic way to test the completed MDA optical module as it leaves the manufacturer, arrives at a test facility and is installed in an MDA device.